Exception during wordcount in Hadoop

Question

I have installed Hadoop successfully and now I want to run Wordcount.jar . As shown below, my source address is /user/amir/dft/pg5000.txt and destination address to save results is /user/amir/dft/output.txt .

I have downloaded the .jar file from this url . Now I'm facing this error message when I run the below command. I followed the instructions found at this url and now my problem is on "Run the MapReduce job" step. How can I overcome it?

amir@amir-Aspire-5820TG:/usr/local/hadoop$ bin/hadoop jar /usr/local/hadoop/wordcount.jar wordcount /user/amir/dft/pg5000.txt /user/amir/dft/output.txt
Exception in thread "main" java.lang.ClassNotFoundException: wordcount
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:270)
at org.apache.hadoop.util.RunJar.main(RunJar.java:205)
amir@amir-Aspire-5820TG:/usr/local/hadoop$ 

Answer 1

It means u have a typo or somthing wrong with the main class your specifying. Do u mean org.apache.hadoop.examples.WordCount instead of wordcount .

Answer 2

You don't need to download a new .jar file. A wordcount jar is already there in the examples of hadoop. Just use the command:

bin/hadoop jar hadoop*examples*.jar wordcount  /user/amir/dft /user/amir/dft-output

The input and output paths should be directories on HDFS, not files. This will run the wordcount program on all the files that are uploaded on HDFS under the /user/amir/dft/ path, (including your pg5000.txt file).

EDIT : If you want to run this specific jar that you have downloaded, though, follow @samthebest's answer (keeping in mind that the input&output paths are directories).

EDIT2 : Following the comments of this answer, it seems that the hadoop version used is newer than the one described in the tutorial. So the .jar for the wordcount program is located at the path hadoop_root/share/hadoop/mapreduce/hadoop-mapreduce-examples-2.2.0.jar , as mentioned in this post .